Projection-space methods to take into account finite beam-width effects in two-dimensional tomography algorithms

Detection systems used for computerized tomography are often approximated by line integrals, despite having non-negligible beam widths due to a finite detector size and a finite acceptance angle. Ways to take into account these beam widths in algorithms for two-dimensional straight-line emission tomography are discussed. It is shown that the full three-dimensional imaging properties of the detection system, including filter functions, can be described in projection space. The relationships with the geometric matrix and the etendue are discussed. Two methods to compensate for most of the beam-width effects have been developed, which can be combined with many tomography algorithms. The two methods are demonstrated to improve the quality of tomographic reconstructions of measurements by the bolometer tomography system on the JET (Joint European Torus) tokamak. The strengths and limitations of the methods are discussed. (author)